The present invention relates to a run flat pneumatic radial tire and more particularly to a pneumatic radial tire having an improved durability in run flat traveling.
A run flat pneumatic tire is a tire constructed so that the tire can continue traveling a certain distance even after the internal pressure is decreased due to occurrence of puncture. In the conventional run flat pneumatic tire, the rigidity of the side wall portion is increased as high as possible to render the tire difficult to bend, thereby imparting a run flat performance to the tire.
From the viewpoint of the fact that the lower the flatness of the tire, the easier the increase in the rigidity of the side wall portion to render the tire difficult to bend, Japanese patent application Kokai Publication No. 64-30809 proposes a run flat pneumatic tire wherein a reinforcing liner comprising a high-hardness rubber and having a crescent cross section is disposed on the inside of the side wall portion of a tire having a flatness of 55% or less in such a manner that the upper end and the lower end of the reinforcing liner overlap with a belt layer and a bead filler, respectively. In the above, described run flat pneumatic tire having a small flatness, however, since the height of the side wall portion is small, a flex strain is locally increased in a region from around the upper end of a rim flange to around the end of a belt edge, so that cracks tend to occur in an inner liner layer covering the inside of the reinforcing layer and mainly composed of a butyl rubber. Further, the durability in run flat traveling is unfavorably reduced because the insides of the inner liner layer are rubbed against each other during flexing to bring about an abrasion.